The number of drug-related killings in the Philippines since President Rodrigo Duterte took power has doubled to about 1,800, with the controversial leader lashing out over United Nations' criticism of the deaths.

However, Mr Duterte's foreign minister Perfecto Yasay today said the Philippines would remain a UN member and described the President's comments as expressions of "profound disappointment and frustration".

"We are committed to the UN despite our numerous frustrations and disappointments with the international agency," Mr Yasay told a news conference.

Mr Yasay said the President has promised to uphold human rights in the fight against drugs and has ordered the police to investigate and prosecute offenders.

He criticised the UN rapporteurs for "jumping to an arbitrary conclusion that we have violated human rights of people".

"It is highly irresponsible on their part to solely rely on such allegations based on information from unnamed sources without proper substantiation," Mr Yasay said.